Under the influence of the monsoons, Iraq in summer has a constant northwesterly wind (shamal), while in winter a strong southeasterly air current (sharqi) develops. The intensely hot and dry summers last from May to October, and during the hottest time of the day—often reaching 49° C (120° F ) in the shade— people take refuge in underground shelters. Winters, lasting from December to March, are damp and comparatively cold, with temperatures averaging about 10° C (50° F ). Spring and autumn are brief transition periods. Normally, no rain falls from the end of May to the end of September. With annual rainfall of less than 38 cm (15 in), agriculture is dependent on irrigation.